Virtual memory management for real-time embedded devices

ABSTRACT

An apparatus comprising an arbiter circuit, a translation circuit and a controller circuit. The arbiter circuit may be configured to generate one or more first control signals and a data write signal in response to an input signal and a read data signal. The translation circuit may be configured to generate a one or more second control signals in response to the one or more first control signals and the write address signal. The controller circuit may be configured to generate an address signal in response to the one or more second control signals.

FIELD OF THE INVENTION

The present invention relates to memory management generally and, moreparticularly, to a method and/or architecture for implementing virtualmemory management in real-time embedded devices.

BACKGROUND OF THE INVENTION

Conventional mobile devices increasingly serve many functions such ascellular phone calling, Internet or wi-fi access, general purposegraphical applications, video and/or image processing. Each of theseapplications use system resources differently. Future devices areexpected to integrate even more features. Such new features will likelyadd new types of resource requirements and memory patterns.

Application-specific integrated circuits include special-purposehardware units to accelerate critical functions within such hybridsystems. Such hardware units coexist on the same integrated circuit andshare a common pool of systems resources. A host processor typicallyacts as a resource manager by allocating memory for each unit,reclaiming unused or free memory, providing security to preventunauthorized access to memory contents, and managing power usage.Depending on the overall system requirements, the resource manager canalso operate as a collection of host processors.

Conventional operating systems use virtual memory to provide a singleinterface to each program. Such an approach provides the illusion to theclient of having a contiguous block of memory addresses. However, theaddresses are fragmented in a physical storage device (i.e., DRAM, FLASHcard, or an external storage devices, etc.). Virtual memory systemstranslate virtual memory addresses to physical memory accesses viavirtual to physical table lookups.

Modern virtual memory systems are sometimes separate virtual andphysical memory into blocks of a fixed or variable size called pages.When a program accesses a new virtual page, the host processor accessesthe page table to translate the virtual page number (VPN) to a physicalpage number (PPN) to construct the physical address and access thecorrect location in memory. Page-table lookups are time-intensiveoperations. Modern processors provide a cache of virtual to physicaltranslations for the host-processor. This cache is sometimes referred toas an address translation cache or translation look-aside buffer (TLB).

Clients also need to access physical memory, either to perform specificfunctions or to execute proxy transfers for the host (i.e., DirectMemory Access (DMA)). If clients access physical storage through virtualmemory, such clients need to access the TLB directly or to keep shadowcopies of the TLB entires locally to keep the mapping tables of thevarious clients consistent. In both cases, clients use a page tablelookup operation to find new pages or pages no longer found in the TLB.Communication occurs from the host to the clients when the host changesvirtual to physical translations.

However, clients often have real-time deadlines that must be met tooperate properly. These deadlines are especially important in digitalimage and video processing, medical devices, aeronautical systems,automobiles or other mechanical control systems where real-timedeadlines are critical. Missing a deadline in these cases can lead toimage corruption, data inaccuracies, or other system errors withdisastrous consequences. Memory space used by these devices does notgenerally fit in the TLB exclusively (i.e., page table lookups areneeded when page-table entries are not found in the buffer).

Clients with real-time constraints typically cannot leverage TLBsbecause a page-table access is too expensive and unpredictable. Too manypage table lookups can stall the client, potentially causing a misseddeadline. Modern real-time systems attempt to solve this problem bysupporting physical-only memory accesses exclusively or splittingphysical storage between physical-only access for clients andvirtual-only memory access for general-purpose applications.

The first approach drops key benefits of virtual memory. The secondapproach creates a sub-optimal allocation of system storage because thedivision is static and cannot easily adjust if the system migrates fromrunning general-purpose applications to real-time applications or visaversa.

It would be desirable to implement a host processor to provide thebenefits of virtual memory while allowing real-time clients to meetperformance deadlines.

SUMMARY OF THE INVENTION

The present invention concerns an apparatus comprising an arbitercircuit, a translation circuit and a controller circuit. The arbitercircuit may be configured to generate one or more first control signalsand a data write signal in response to an input signal and a read datasignal. The translation circuit may be configured to generate a one ormore second control signals in response to the one or more first controlsignals and the write address signal. The controller circuit may beconfigured to generate an address signal in response to the one or moresecond control signals.

The objects, features and advantages of the present invention includeproviding a memory management system that may (i) operate with real-timeembedded devices, (ii) allow clients to manage one or more particularresources without access to a host processor, (iii) provide virtualmemory access to all clients in the system, regardless of real-timedeadlines, (iv) create a common intermediate translation memory spacethat may be partitioned by a host and/or (v) introduce a virtual spacefor clients of the host processor to manage according to a current workset.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andthe appended claims and drawings in which:

FIG. 1 is a diagram illustrating three key address spaces used to allowclients to manage individual virtual memory spaces;

FIG. 2 is a block diagram illustrating the placement of the ATT lookuptable in a DRAM controller;

FIG. 3 is a block diagram illustrating a CVPN to PPN lookup table withinthe ATT; and

FIG. 4 is a block diagram illustrating the client segment tableprogrammed by the host processor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may relate to a system on a chip with a main hostprocessor managing a collection of specialized functional units orcoprocessors. The specialized functional units may have differentresources and/or access memory in unique ways.

The techniques and implementation described allow an individual clientto manage one or more particular memory resources without needing accessto the host processor.

The present invention may implement a host processor to provide virtualmemory access to some or all of the clients in the system, regardless ofreal-time deadlines. Management of the timing of page table lookups maybe controlled either by the host or by one or more of the individualclients. The host may set aside a segment of virtual memory for use bythe client and may maintain a page table of VPN to PPN translations forthe virtual segment in a physical storage device, similar to typicalvirtual memory systems.

Unlike a translation lookaside buffer or an address translation cache,the present invention may create a common intermediate translationmemory space that a host partitions into segments. The segments may beindependently accessible by each client. An address translation table(ATT) may be implemented to hold the mapping from the translation memoryspace to the physical memory space. The size of the translation memoryspace is normally determined by multiplying the number of entries in thetranslation table by the page size. If the translation memory space islarger than the entries in the ATT, then each client maps a portion of arespective segment into the ATT. The size of the memory space isdetermined by the number of CVPN bits in the ATT. In addition, eachclient may have an ATT and a respective ATT address space.

The individual clients may control the exact mapping of a respectivevirtual segment to physical memory by updating entries in the addresstranslation table depending on current working sets. Such a transfer ofcontrol may allow the client to explicitly manage timing of expensivepage table lookup operations.

The present invention may introduce a virtual space for clients of thehost processor to manage according to a current working set. The hostmay partition the virtual space for each client into separate segmentsusable for each respective client. In one embodiment, the virtual spacemay be universal among all clients and/or may be separate from thevirtual memory space of processes running on the host. Alternativevirtual memory approaches include implementing separate virtual addressspaces for subsets of the clients and/or implementing one virtual spaceper client.

Referring to FIG. 1, a diagram of a memory arrangement 100 is shown. Thearrangement 100 includes an address translation table (ATT) 102, amemory space 104, a memory space 106, a memory space 108, and atranslation look aside buffer (TLB) 110. The memory space 104 may beimplemented as a host virtual memory space. The memory space 106 may beimplemented as a client virtual memory space. The memory space 108 maybe implemented as a physical memory space. The address translation table102 may be implemented in hardware, software, or a combination ofhardware and/or software. A number of clients 120 a-120 n may access theclient virtual memory space. The address translation table 102 may belocated on a chip that maps the virtual pages of the clients 120 a-120 nto physical pages in the address translation table 102. A host 130 (orhost processor) may access the host virtual memory space. The individualclients 120 a-120 n may index the address translation table 102 with avirtual page number (CVPN) of a particular client to find thecorresponding physical page number (PPN) of the physical memory space108. The physical memory space 108 generally comprises a host page table130, a PPN section 132, a message area 134, a PPN area 136, a clientpage list 138, and a PPN area 140.

The virtual-to-physical lookup of the buffer 110 may operate in parallelto a memory organization protocol used by the host processor 130. Theparticular addressing protocol used by the host processor 130 may beimplemented using a variety of techniques. The virtual-to-physicallook-up of the buffer 110 may be implemented in addition to the memoryorganization protocol used by the host processor 130. The host processor130 may translate host virtual page numbers (HVPN) to physical pagenumbers (PPN) using traditional virtual memory. The host processor 130may also access the physical memory 108 directly without a virtualmemory scheme.

Communication between the host processor 130 and the clients 120 a-120 n(to be described in more detail in connection with FIG. 2) may occurthrough point-to-point connections, messages through a proxy, sharing amessage area 134 in physical storage visible to both the host processor130 and the clients 120 a-120 n, etc. Communication through the physicalmemory 108 may be implemented by one of the clients 120 a-102 naccessing the physical memory space 108 directly, by bypassing the ATT102, or by mapping the message area 134 to a virtual page within asegment of the physical memory space 108. In the latter case, the hostprocessor 130 may also map one or more physical pages in the messagearea 134 to the virtual memory space 104 of the host processor 130. Boththe host processor 130 and the clients 120 a-120 n need to clear updatesor writes to the message area 134 in the physical memory space 108 forcommunication to occur. Caching and/or buffering by either the host 130or one or more of the clients 120 a-120 n hides the communication. Asnoop protocol, message passing protocol, a direct wire communication,or any other mechanism to send updates to the clients 120 a-120 n fromthe host 130, or visa versa, may be implemented. Such a protocol mayavoid the communicating agents (either the host 130 or one or more ofthe clients 120 a-120 n) from repeatedly polling the content of thememory 108 to detect new messages. For example, the page PPNj (136) maybe used to communicate, since both the clients 120 a-120 n and the host130 may access the page PPNj (136).

The memory arrangement 100 may include a number of registers 114. Theregisters 114 store a configuration state for client segments and theCVPN-to-PPN mappings. The registers 114 may be accessible in thephysical address space. In one example, the registers 114 may beimplemented as specialized control registers rather than general purposeregisters found on a processor. The mapping may be a function of thecontent of the registers 114 and the address translation table 102. Oneor more of the clients 120 a-120 n may have physical-only access. One ormore of the clients 120 a-120 n may snoop and/or read the controlregisters 114 for debugging, to aid communication, or for anotheradaptive operation. One or more of the clients 120 a-120 n may also readthe mappings from another one of the clients 120 a-120 n to determinetranslations. In one operating mode of the memory arrangement 100, thehost processor 130 may allocate a segment within the virtual memoryspace 106 when enabling a particular one of the clients 120 a-120 n. Thehost processor 130 may then generate a list of physical pages for use bythe particular one of the clients 120 a-120 n. The physical pages (e.g.,132, 136, 140, etc.) may not need to be contiguously located in thephysical storage 108. The host processor 130 may communicate to each ofthe clients 120 a-120 n the range of the virtual segments used for eachof the clients 120 a-120 n and the list of physical pages (e.g., 132,136, 140, etc.) to use.

Once the host processor 130 finishes the configuration, the selected oneof the clients (e.g., 120 a) maps physical pages in a current workingset to a particular CVPN page (e.g., CVPNa) in a virtual segment (e.g.,PPNa). The client 120 a may then update the ATT 102 with each newCVPN-to-PPN mapping. The columns shown in the ATT 102 illustrate theCVPN-to-PPN mapping. The client 120 a then uses virtual addresses toaccess physical storage 108. As the current working set changes overtime, the client 120 a may free virtual pages that are no longer in theworking set and may update the freed entries of the ATT 102 to map newphysical pages. The client 120 a may hold a small set of page listswithin the ATT 102 and may control the timing of working set changes.The host processor 130 may be configured to leave the physical page listof a particular one of the clients 120 a-120 n unchanged until theclient completes execution or acknowledges a release request of thelist. In general, the host page table list 130 and client page list 138in the physical memory space 108 will be larger than the storage of theTLB 110 and the ATT 102.

A particular client (e.g., 120 a) may manage the client segment. Otherclients (e.g., 120 b-120 n) or the host processor 130 may also managethe client segment on behalf of the client 120 a. Client segmentmanagers should normally have read and write access to the registers 114to change the client 120 a table entries in the ATT 102. The page listPPNa-PPNn (138) may be shared with the client segment manager. In oneexample, the page list PPNa-PPNn (138) may be globally visible to theclients 120 a-120 n or exclusively shared with the client segmentmanagers.

In another operating mode, the clients 120 a-120 n may access thephysical memory 108 directly and bypass the lookup in the ATT 102. Theclients 120 a-120 n operating in this mode may be referred to asphysical clients. The clients 120 a-120 n operating as physical clientsdo not access the virtual memory 106. By contrast, the clients 120 a-120n operating as virtual clients may access the ATT 102 to translatevirtual addresses to the physical memory 108.

The arrangement may cover the described operating modes for any of theclients 120 a-120 n. The host processor 130 may select the operatingmode for each of the clients 120 a-120 n by setting controller registersin the memory controller (to be described in more detail in connectionwith FIG. 2). These registers may allow a user to select the type ofmemory access that best fits each of the needs of each of the particularclients 120 a-120 n.

Referring to FIG. 2, a block diagram of a system 200 is shown inaccordance with an embodiment of the present invention. The system 200generally comprises a number of clients 202 a-202 n, a block (orcircuit) 204, a block (or circuit) 102, a block (or circuit) 208, and ablock (or circuit) 210. The circuit 204 may be implemented as an arbitercircuit. The circuit 102 may be implemented as an address translationtable circuit. The circuit 208 may be implemented as a controllercircuit. The circuit 210 may be implemented as a physical storagedevice. The circuit 210 generally corresponds to the memory 108 ofFIG. 1. The clients 202 a-202 n generally correspond to the clients 102a-102 n of FIG. 1. The circuit 204 may have an input 220 that mayreceive a signal (e.g., IN), an input 222 that may receive a signal(e.g., READ_DATA), an output 224 that may present a signal (e.g.,WRITE_DATA), an output 226 that may present a signal (e.g.,CLIENT_ADDRESS), and an output 228 that may present a signal (e.g.,CLIENT_ID).

The circuit 102 may have an input 230 that may receive the signalCLIENT_ID, an input 232 that may receive the signal CLIENT_ADDRESS, aninput 234 that may receive the signal WRITE_DATA, an output 236 that maypresent a signal (e.g., PHYSICAL_ADDRESS), and an output 238 that maypresent a signal (e.g., VALID).

The circuit 208 may have an input 240 that may receive the signal VALID,an input 242 that may receive the signal PHYSICAL_ADDRESS, and an output244 that may present a signal (e.g., ADDR). The circuit 210 may have aninput 246 that may receive the signal ADDR, an input 248 that mayreceive the signal WRITE_DATA, and an output 250 that may present thesignal READ_DATA.

The system 200 illustrates how the memory arrangement 100 interfaceswith other components in a typical controller used to access the offchipmemory 210. The clients 202 a-202 n may send a request for physicalstorage to the arbiter 204 using a virtual address. The arbiter 204 maythen choose which request to schedule based on a predeterminedscheduling scheme. The arbiter 204 may then send the signal CLIENT_IDand CLIENT_ADDRESS to the ATT circuit 102. The ATT circuit 102 may thenconstruct the signal PHYSICAL_ADDRESS from this information and may markthe signal VALID as valid or invalid depending on the signalCLIENT_ADDRESS. The controller 208 may then send the signal ADDR to thephysical storage 210, discard invalid requests and update error statusregisters accordingly. The translation may also occur beforearbitration. In this case, the ATT 102 may be part of one or more of theclients 202 a-202 n. In such an implementation, the ATT 102 may berestricted to generating physical accesses when communicating with thearbiter 204 and/or controller 208. The clients 202 a-202 n are notgenerally restricted from using virtual memory internally. Thecontroller 208 does not normally perform address translations.

The ATT circuit 102 may support both virtual and physical clients.Physical clients access physical memory directly (e.g., withouttranslation) and virtual clients access an address translation table totranslate the virtual page number (CVPN) of a particular client 202a-202 n to a physical page number (PPN). Virtual client accesses may beguarded by a CVPN base and an upper bound. The ATT circuit 102 may markany access above or below the bounds as invalid, signal the controller208 to prevent the invalid access (either a read or a write) fromaccessing the physical memory 210, and/or send an interrupt to the hostprocessor 130 for error handling. The host processor 130 may enable,disable, and/or ignore interrupts generated by segmentation violations.In physical clients, the CVPN may be equal to the PPN.

Referring to FIG. 3, a more detailed diagram of the ATT circuit 102 isshown illustrating the process of translating a CVPN to a PPN. The ATTcircuit 102 generally comprises a block (or circuit) 302, a block (orcircuit) 304, a block (or circuit) 306, a block (or circuit) 308, ablock (or circuit) 310, a block (or circuit) 312, a block (or circuit)314, and a block (or circuit) 316. The circuit 302 may be implemented asa client segment table. The circuit 304 may be configured to store aCVPN. The circuit 306 may be implemented as a block configured to storea PPN. The circuit 308 may be implemented as a selection circuit. Thecircuit 310 may be implemented as a page number table. The circuit 312may be implemented as an error checking circuit. The circuit 314 may beimplemented as a page offset. The circuit 316 may be implemented as apage offset.

When one of the clients 202 a-202 n accesses the memory 210, theparticular client (e.g., 202 a) may issue a memory request to thearbiter 204, which forwards the request to the ATT circuit 102. The newrequest arrives as a block of data including a unique identifier of theparticular client 202 a and a virtual address, separated into the CVPN304 and the page offset 314 into the current page. The page offset 314normally remains unchanged from the CVPN 304 to the PPN 306, thus thepages offset field typically remains constant. The ATT 102 may use theclient ID to lookup the entry of the client 202 a in the client segmenttable 118 (to be described in more detail in connection with FIG. 4).The ATT 102 may also check for valid access. If a bypass bit is set (tobe described in more detail in connection with FIG. 4), the client 202 ahas physical access privileges and the CVPN equals the PPN withouttranslation or access privilege checking. If the bypass bit is not set,and the CVPN is valid, the ATT 102 uses the CVPN to index the physicalpage number table 310 and read the new PPN if the CVPN falls within thevirtual segment of the particular client 202 a.

The memory arrangement 100 may include an optional error status state toindicate to the host processor 130 that an illegal access has occurred.Error status registers, violation address registers, and violationclient ID registers may be implemented to provide the type of invalidaccess, the address that accessed memory outside of its segment, and/orthe client ID that generated the invalid access respectively. The memoryarrangement 100 may cover scenarios that may occur when the memoryarrangement 100 records no invalid access, a single invalid access, or alist of invalid accesses. The memory arrangement 100 may replace and/orsupplement other virtual memory implementations. If an error occursduring a memory access, such as an invalid CVPN, the error checkingcircuit 312 may record the error in an error status register containedwithin the error checking circuit 312. In addition, the error statusregister may record the CVPN 304, the PPN 306 and/or the ID of theclient that caused the error. The error checking circuit 312 may alsogenerate an error interrupt to the host processor 130. Recording errorsand generating an error interrupt to the host processor 130 may be usedfor error recovery or for debugging purposes.

An access privilege may also be specified on a per memory request basis.For example, the bypass bit may be stored as a field in the memoryrequest. Memory requests with the bypass bit set may act as a physicalclient. Such a per-request control may replace or act in conjunctionwith the per-client bypass bit.

The PPN table 310 may be controlled by either the host 130 or one of theclients 120 a-120 n. Each of the clients 120 a-120 n in the addresstranslation table 102 may optionally include an enable bit in additionto a bypass bit. One or more of the clients 120 a-120 n may be disabled.Such a disabled one of the clients 120 a-120 n may still use the ATT102, but may copy the value of the CVPN block 304 to the PPN block 306and not provide range checking of addresses. The disabled virtualclients 120 a-120 n may act like physical clients. The resulting valuestored in the PPN block 306 may then be recombined with the page offset316 to form a physical address to access physical storage 210 or theregisters 114.

The ATT 102 may contain a fixed number of entries. The number of entriesmay restrict how many mappings the clients 202 a-202 n may bufferwithout implementing a page-table lookup. The signals CLIENT_ID andCLIENT_ADDRESS may be used to determine if a potential new access to thememory 108 (or 210) is a virtual access or a physical access (e.g.,using the signal BYPASS_TRANSLATION). If the new access is virtual, thesignal PAGE_INDEX may determine which entry contains the VPN to PPNmapping in the ATT 102. This calculation may be done by looking up theclient segment table 302. The signal PAGE_INDEX may be the address ofthe correct physical page number for the virtual page number of arequestor within the ATT 102. The PPN block 306 may receive the physicalpage number, the data returned by reading the signal PAGE_INDEX addresswithin the ATT table 102. The access of the ATT table 102 may occurwhether the translation is valid or not. For example, if the bypass bitis set, the entry read from the ATT 102 may be ignored. Such anoperation may be determined by the following equation EQ1:PPN=if(bypass)CVPN else ATT[PAGE_INDEX];  EQ1

Referring to FIG. 4, a more detailed diagram of the client segment table302 is shown. The client segment table 302 generally comprises a CVPNbase column, a CVPN bound column, a bypass column, a block (or circuit)402 and a block (or circuit) 404. The circuit 402 may be implemented asa greater than logic circuit. The circuit 404 may be implemented as agreater than logic circuit. The client segment table 302 may hold accessprivileges (e.g., virtual, physical, etc.) as the signal VALID and arange of each virtual segment of a particular client 202 a-202 n. Thesignal VALID is invalid if the virtual address is outside the range ofthe virtual segment. If one of the clients 202 a-202 n does not havedirect access to the ATT 102, the host 130 or another one of the clients202 a-202 n that has access to the ATT 102 may control the clientvirtual memory space 106 by sending updates to the ATT 102. The hostprocessor 130 may allocate a segment of the client virtual memory space106 for a new one of the clients 202 a-202 n and then determine theaccess privilege of each of the clients 202 a-202 n.

The CVPN base bits may correspond to the starting address of thesegment. The CVPN bound bits may be the CVPN base plus the size of thesegment. The bypass bit, which is part of the registers 114, isgenerally set true (e.g., ON) if a particular one of the clients 202a-202 n is physical. The bypass bit is generally set false (e.g., OFF)if a particular one of the clients 202 a-202 n is virtual. The registers114 are memory mapped to a portion of the physical memory space 108.When the ATT 102 receives a translated or non-translated physicalaccess, the physical access is not sent to the physical storage 108.Instead, the registers 114 within the ATT 102 are utilized. The hostprocessor 130 normally also has access to the same memory mapped portionto control the ATT 102 properly. Therefore, the host 130 then sends thebypass bits to the client segment table 302 by issuing a store operationto the registers 114.

In one example, the bypass bit column may be implemented in a separateregister (not shown). In another example, if none of the clients 202a-202 n need direct physical access, the bypass bit may not be needed.The particular polarity of the bypass bit may be varied to meet thedesign criteria of a particular implementation.

The client segment table 302 may use greater than or less than logic inthe blocks 402 or 404 to check for “in range” accesses. Alternativeimplementations of the client segment table 302 may include using a baseaddress and a size to specify a particular client segment. If aparticular access is invalid, the calculated physical page number may beignored or recorded as a segmentation violation address. For example,the translation may be calculated to determine whether the access isinvalid or not.

The various signals of the present invention are generally “on” (e.g., adigital HIGH, a “true” or 1) or “off” (e.g., a digital LOW, a “false” or0). However, the particular polarities of the on (e.g., asserted) andoff (e.g., de-asserted) states of the signals may be adjusted (e.g.,reversed) to meet the design criteria of a particular implementation.Additionally, inverters may be added to change a particular polarity ofthe signals.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

The invention claimed is:
 1. An apparatus comprising: a plurality ofclient devices; an arbiter circuit configured to (i) arbitrate amongsaid client devices to access a storage device and (ii) generate all of(a) one or more first control signals, and (b) a data write signal inresponse to an input signal received from a particular one of saidclient devices that wins said arbitration; a translation circuitconfigured to generate one or more second control signals in response tosaid first control signals to translate a virtual address into aphysical address; a controller circuit configured to generate an addresssignal that conveys said physical address in response to said secondcontrol signals; and a host configured to program said translation intosaid translation circuit.
 2. The apparatus according to claim 1, whereinsaid address signal is used by said storage device to store dataconveyed in said data write signal.
 3. The apparatus according to claim1, wherein said storage device comprises a single memory space shared byall of said client devices and said host.
 4. The apparatus according toclaim 1, wherein said input signal received from said particular clientdevice includes said virtual address.
 5. The apparatus according toclaim 1, wherein (i) said host is further configured to allocate asegment within said translation circuit to said Particular client deviceand (ii) said segment controls access to said storage device by saidparticular client device.
 6. The apparatus according to claim 5, whereinsaid particular client device, other ones of said client devices, orsaid host manages said segment allocated to said particular clientdevice.
 7. The apparatus according to claim 1, wherein said translationcircuit is further configured to pass said virtual address through assaid physical address such that said particular client device directlyaccesses said storage device.
 8. The apparatus according to claim 1,wherein (i) said translation circuit includes a table that defines anintermediate memory space common to all of said client devices, (ii)said intermediate memory space is partitioned into a plurality ofsegments and (iii) each one of said segments is accessed by a respectiveone of said client devices.
 9. The apparatus according to claim 8,wherein said segments in said translation circuit are updated dependingon current working sets to free one or more of a plurality of virtualpages no longer being used by said client devices.
 10. A method forvirtual memory management, comprising the steps of: (A) arbitratingamong a plurality of client devices to access a storage device; (B)generating in an arbitration circuit all of (i) one or more firstcontrol signals and (ii) a data write signal in response to an inputsignal received from a particular one of said client devices that winssaid arbitration; (C) generating in a translation circuit one or moresecond control signals in response to said first control signals totranslate a virtual address into a physical address; (D) generating in acontroller circuit an address signal that conveys said physical addressin response to said second control signals; and (E) programming saidtranslation into said translation circuit from a host.
 11. The methodaccording to claim 10, further comprising the step of: allocating asegment within said translation circuit to said particular clientdevice, wherein said segment controls access to said storage device bysaid particular client device.
 12. The method according to claim 11,wherein said particular client device, other ones of said clientdevices, or a host manages said segment allocated to said particularclient device.
 13. The method according to claim 10, further comprisingthe step of: passing said virtual address through said translationcircuit as said physical address such that said particular client devicedirectly accesses said storage device.
 14. The method according to claim10, wherein (i) said translation circuit includes a table that definesan intermediate memory space common to all of said client devices, (ii)said intermediate memory space is partitioned into a plurality ofsegments and (iii) each one of said segments is accessed by a respectiveone of said client devices.
 15. The method according to claim 14,further comprising the step of: updating said segments in saidtranslation circuit depending on current working sets to free one ormore of a plurality of virtual pages no longer being used by said clientdevices.